Hitherto known cranes in forest machines of the above-described type normally comprise not only a crane post and an outer boom, but also a first boom section which is mounted therebetween and the movements of which are adjusted by means of at least one hydraulic cylinder. This means that it is difficult to maneuver such cranes when operating in forest stands where it is desirable in as short a time as possible to seize and/or process the trees and place them on the load carrier of the machine, since the operator must pay attention not only to such functions as the rotation of the crane post, pivotal movement of the outer boom and telescopic movement of the extension boom in relation to the outer boom, but also to the movements of the first boom section in relation to the crane post as well as the cooperation of the first boom section with the outer boom. Another shortcoming inherent in prior art cranes of the above type is that they are of a complicated and, thus, expensive design.